1. Field of the Invention
The present invention relates to a radiation sensitive composition comprising as essential components
a) a polymer (a matrix resin) which is insoluble in water but is soluble in or at least swellable in an aqueous alkaline solution,
b) a compound cleavable with an acid or b') a compound crosslinkable using an acid,
c) a compound capable of forming an acid upon exposure to actinic radiation, and
d) a radiation sensitive base, for stabilizing the width of lines, in combination with the components a), b), and c) or alternatively the components a), b'), and c).
Further, the present invention relates also to a photoresist and an electronic component produced from the above composition, production of a printing plate, and a radiation sensitive copying material.
2. Description of the Related Art
An ever-increasing tendency toward a reduction in structural dimension (for example, in the production of chips) has necessitated an improvement in a lithographic technique in a region of less than 1 .mu.m. In such a technique, high energy UV light, electron beams, and X rays are used for exposure. The improvement in the lithography has brought about a change in requirements which radiation sensitive compositions should meet. These requirements are described in, for example, C. G. Wilson, "Organic Resist Materials-Theory and Chemistry" [Introduction to Microlithography, Theory, Materials, and Processing, edited by L. F. Thompson, C. G. Wilson, M. J. Bowden, ACS Symp. Ser., 219, 87 (1983), American Chemical Society, Washington]. Specifically, there is an increasing demand for radiation sensitive composition which are preferably sensitive to a wide region of spectrum and, hence, applicable to not only the conventional photolithography but also advanced lithographic techniques, such as near UV, far UV, deep UV, electron beam, or X-ray lithography, without sacrificing the sensitivity.
A chemically sensitized resist, which has been for the first time disclosed by Ito et al. [H. Ito and C. G. Wilson, Polym. Eng. Sci., Vol. 23, 1012 (1983)], has been extensively used for the production of a radiation sensitive mixture having a high sensitivity to high energy radiation. In general, protons generated during irradiation are catalytically reacted at room temperature or a temperature above room temperature depending upon the chemical composition of the radiation sensitive mixture. This catalytic reaction imparts a high sensitivity to the radiation sensitive mixture.
In the semiconductor industry, a radiation sensitive composition (hereinafter often referred to as "resist material" or "resist blend") should be developable with an alkaline solution. Preferably, the alkaline solution is an organic base solution, such as 2 to 3% aqueous solution of tetramethylammonium hydroxide (TMAH).
A novolak resin or a homopolymer or a copolymer of vinyl phenol is best suited for this purpose. For photolithography, the use of novolak is limited to the case where the radiation has a longer wavelength than 300 nm because novolak has a high absorption in shorter wavelengths. Adverse effect of absorbance causes the resist image to have such a profile that the wall is extremely inclined. The vinylphenolic resin can be used in deep UV lithography when it has a combination of desired dissolution properties with high optical transparency. Poly(4-vinylphenol), when used alone, exhibits a considerably high dissolution rate and, therefore, as such, is not suitable for the above purpose. One of the methods for lowering the dissolution rate to a desired value is to copolymerize 4-vinylphenol with other alkyl-substituted phenols. Such copolymers are described in European Patent Nos. 0307752 and 0307751 and Japanese Patent Laid-Open No. 166105/1990. Other copolymers of 4-hydroxystyrene, although is independently of the solubility thereof in an aqueous alkaline solution, are described by Maruzen Petrochemical Co., Ltd. in "Kobunshi," Vol. 38,571 (1989).
Basically, alkali-soluble poly(4-vinylphenol) and copolymers thereof may be used as a radiation sensitive composition by two methods. One of the methods is to add a protective group, cleavable with an acid, to hydroxyl groups in such a manner that the protective group is added to all the hydroxyl groups to render the polymer insoluble or alternatively to part of the hydroxyl groups. A mixture of such a protected polymer and a photo-acid generator, which will be described later, is prepared. This mixture, when irradiated with actinic radiation, generates an acid which eliminates the protective group sensitive to the acid. The protective group include tert-butyloxycarbonyloxy or its derivatives (Ito et al., J. Photopolym. Sci. & Tech., Vol. 6, No. 4, 1993, p. 547) and a tetrahydropyranyl group (Hattori et al., J. Photopolym. Sci. & Tech., Vol. 6, No. 4, 1993, p. 497). Another method is to mix the alkali-soluble poly(4-vinylphenol) or copolymers thereof with a dissolution inhibitor sensitive to an acid, such as polyacetals described in Pawlowski et al., J. Photopolym. Sci. & Tech., Vol. 15, No. 1 (1992) p. 55. This mixture is insoluble in an aqueous alkaline developer before exposure. The exposure thereof to deep UV light, however, brings about cleavage of the dissolution inhibitor, rendering the mixture soluble in the alkaline developer.
Compounds capable of generating an acid upon exposure to actinic radiation, for example, onium salts, such as a phosphonium salt, a sulfonium salt, and an iodonium salt of non-nucleophilic acids, such as HSbF.sub.6 and HAsF.sub.6, have hitherto been used as described in J. V. Crivello, Polym. Eng. Sci., 23 (1983) 953. Further, halogen compounds, particularly trichloromethyltriazine derivatives or trichloromethyloxadiazole derivatives, o-quinonediazide sulfonylchloride, o-quinonediazide-4-sulfonate, a combination of an organometal/an organohalogen, bis(sulfonyl)diazomethane, sulfonylcarbonyldiazomethane (DE-A 3,930,087), and nitrobenzyl tosylate are recommended in F. M. Houlian et al., SPIE Proc., Adv. in Resist Tech. and Proc. 920 (1988) 67.
The radiation sensitive composition may contain, in addition to the above compounds, other additives for enhancing the contrast and controlling a reduction in line width.
It is important for the radiation sensitive composition to have high transparency, good adhesion to a substrate, good pattern profile after development, low standing waves, good heat stability, and etching resistance. A single mixture constituting such a composition is unavailable. Therefore, resist materials, which can overcome the above problems, can be put to practical use, and have high sensitivity, have been desired in the art.
An object of the present invention is to provide both positive and negative radiation sensitive compositions, particularly resist materials, which have high transparency to deep UV light, such as KrF excimer laser beam, high sensitivity to these light sources, electron beams, and X rays, excellent heat resistance, excellent adhesion to substrates, undergo no change in dimension of patterns with time, and can provide patterns with no standing wave even in fine lines and spaces of less than 0.3 microns.